Method for PDU session establishment procedure and AMF node

ABSTRACT

Provided is a method for handling a packet data unit (PDU) session establishment procedure. The method may performed by an access and mobility management function (AMF) node and comprise: determining whether to reject a PDU session establishment request. The determination may be performed if the PDU session establishment request includes an existing PDU session identifier. Based on the existing PDU session identifier, an identifier of a session management function (SMF) node may be acquired. The PDU session establishment request may be accepted, if it is determined based the identifier of the SMF node that the SMF node and the AMF node belong to a same PLMN. The PDU session establishment request may be further accepted, if it is determined based the identifier of the SMF node that the SMF node belongs to a HPLMN. The PDU session establishment request may be rejected, if it is determined based the identifier of the SMF node that the SMF node and the AMF node do not belong to the same PLMN or the SMF node does not belong to the HPLMN.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application is a continuation ofInternational Application PCT/KR2018/004255, with an internationalfiling date of Apr. 11, 2018, which claims the benefit of U.S.Provisional Patent Applications Nos. 62/486,982 filed on Apr. 19, 2017,62/489,996 filed on Apr. 25, 2017, 62/581,036 filed on Nov. 3, 2017 andKorean Patent Application No. 10-2018-0034808 filed in the KoreanIntellectual Property Office on Mar. 27, 2018, the contents of which arehereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a next generation mobile communication.

Related Art

In 3GPP in which technical standards for mobile communication systemsare established, in order to handle 4th generation communication andseveral related forums and new technologies, research on Long TermEvolution/System Architecture Evolution (LTE/SAE) technology has startedas part of efforts to optimize and improve the performance of 3GPPtechnologies from the end of the year 2004

SAE that has been performed based on 3GPP SA WG2 is research regardingnetwork technology that aims to determine the structure of a network andto support mobility between heterogeneous networks in line with an LTEtask of a 3GPP TSG RAN and is one of recent important standardizationissues of 3GPP. SAE is a task for developing a 3GPP system into a systemthat supports various radio access technologies based on an IP, and thetask has been carried out for the purpose of an optimized packet-basedsystem which minimizes transmission delay with a more improved datatransmission capability.

An Evolved Packet System (EPS) higher level reference model defined in3GPP SA WG2 includes a non-roaming case and roaming cases having variousscenarios, and for details therefor, reference can be made to 3GPPstandard documents TS 23.401 and TS 23.402. A network configuration ofFIG. 1 has been briefly reconfigured from the EPS higher level referencemodel.

FIG. 1 shows the configuration of an evolved mobile communicationnetwork.

An Evolved Packet Core (EPC) may include various elements. FIG. 1illustrates a Serving Gateway (S-GW) 52, a Packet Data Network Gateway(PDN GW) 53, a Mobility Management Entity (MME) 51, a Serving GeneralPacket Radio Service (GPRS) Supporting Node (SGSN), and an enhancedPacket Data Gateway (ePDG) that correspond to some of the variouselements.

The S-GW 52 is an element that operates at a boundary point between aRadio Access Network (RAN) and a core network and has a function ofmaintaining a data path between an eNodeB 22 and the PDN GW 53.Furthermore, if a terminal (or User Equipment (UE) moves in a region inwhich service is provided by the eNodeB 22, the S-GW 52 plays a role ofa local mobility anchor point. That is, for mobility within an E-UTRAN(i.e., a Universal Mobile Telecommunications System (Evolved-UMTS)Terrestrial Radio Access Network defined after 3GPP release-8), packetscan be routed through the S-GW 52. Furthermore, the S-GW 52 may play arole of an anchor point for mobility with another 3GPP network (i.e., aRAN defined prior to 3GPP release-8, for example, a UTRAN or GlobalSystem for Mobile communication (GSM) (GERAN)/Enhanced Data rates forGlobal Evolution (EDGE) Radio Access Network).

The PDN GW (or P-GW) 53 corresponds to the termination point of a datainterface toward a packet data network. The PDN GW 53 can support policyenforcement features, packet filtering, charging support, etc.Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor pointfor mobility management with a 3GPP network and a non-3GPP network(e.g., an unreliable network, such as an Interworking Wireless LocalArea Network (I-WLAN), a Code Division Multiple Access (CDMA) network,or a reliable network, such as WiMax).

In the network configuration of FIG. 1, the S-GW 52 and the PDN GW 53have been illustrated as being separate gateways, but the two gatewaysmay be implemented in accordance with a single gateway configurationoption.

The MME 51 is an element for performing the access of a terminal to anetwork connection and signaling and control functions for supportingthe allocation, tracking, paging, roaming, handover, etc. of networkresources. The MME 51 controls control plane functions related tosubscribers and session management. The MME 51 manages numerous eNodeBs22 and performs conventional signaling for selecting a gateway forhandover to another 2G/3G networks. Furthermore, the MME 51 performsfunctions, such as security procedures, terminal-to-network sessionhandling, and idle terminal location management.

The SGSN handles all packet data, such as a user's mobility managementand authentication for different access 3GPP networks (e.g., a GPRSnetwork and an UTRAN/GERAN).

The ePDG plays a role of a security node for an unreliable non-3GPPnetwork (e.g., an I-WLAN and a Wi-Fi hotspot).

As described with reference to FIG. 1, a terminal (or UE) having an IPcapability can access an IP service network (e.g., IMS), provided by aservice provider (i.e., an operator), via various elements within an EPCbased on non-3GPP access as well as based on 3GPP access.

Furthermore, FIG. 1 shows various reference points (e.g., S1-U andS1-MME). In a 3GPP system, a conceptual link that connects two functionsthat are present in the different function entities of an E-UTRAN and anEPC is called a reference point. Table 1 below defines reference pointsshown in FIG. 1. In addition to the reference points shown in theexample of Table 1, various reference points may be present depending ona network configuration.

TABLE 1 REFERENCE POINT DESCRIPTION S1-MME A reference point for acontrol plane protocol between the E-UTRAN and the MME S1-U A referencepoint between the E-UTRAN and the S-GW for path switching betweeneNodeBs during handover and user plane tunneling per bearer S3 Areference point between the MME and the SGSN that provides the exchangeof pieces of user and bearer information for mobility between 3GPPaccess networks in idle and/or activation state. This reference pointcan be used intra-PLMN or inter-PLMN (e.g. in the case of Inter-PLMNHO). S4 A reference point between the SGW and the SGSN that providesrelated control and mobility support between the 3GPP anchor functionsof a GPRS core and the S-GW. Furthermore, if a direct tunnel is notestablished, the reference point provides user plane tunneling. S5 Areference point that provides user plane tunneling and tunnel managementbetween the S-GW and the PDN GW. The reference point is used for S-GWrelocation due to UE mobility and if the S-GW needs to connect to a non-collocated PDN GW for required PDN connectivity S11 A reference pointbetween the MME and the S-GW SGi A reference point between the PDN GWand the PDN. The PDN may be a public or private PDN external to anoperator or may be an intra-operator PDN, e.g., for the providing of IMSservices. This reference point corresponds to Gi for 3GPP access.

<Next Generation Mobile Communication Network>

Thanks to the success of LTE (Long Term Evolution) and LTE-Advanced(LTE-A) for 4G mobile communication, interest in the next generation,namely 5G mobile communication increases and thus study on the 5G mobilecommunication is progressing.

The 5th generation mobile telecommunications defined by theInternational Telecommunication Union (ITU) refers to communicationproviding a data transmission rate of up to 20 Gbps and an actualminimum transmission rate of at least 100 Mbps anywhere. The officialname of the 5th generation mobile telecommunications is ‘IMT-2020’ andITU's goal is to commercialize the ‘IMT-2020’ worldwide by 2020.

The ITU proposes three usage scenarios, for example, enhanced MobileBroadband (eMBB), massive Machine Type Communication (mMTC) and UltraReliable and Low Latency Communications (URLLC).

First, the URLLC relates to a usage scenario requiring high reliabilityand low latency. For example, services such as automatic driving,factory automation, augmented reality require high reliability and lowlatency (e.g., a delay time of less than 1 ms). The delay time ofcurrent 4G (LTE) is statistically 21 to 43 ms (best 10%) and 33 to 75 ms(median). This is insufficient to support a service requiring a delaytime of 1 ms or less.

Next, the eMBB usage scenario relates to a usage scenario requiringmobile ultra-wideband.

It seems difficult for this ultra-wideband high-speed service to beaccommodated by the core network designed for legacy LTE/LTE-A.

Therefore, in the so-called fifth generation mobile communication, aredesign of the core network is urgently required.

FIG. 2 is an exemplary diagram illustrating a predicted structure of anext generation mobile communication in terms of a node.

Referring to FIG. 2, the UE is connected to a data network (DN) througha next generation RAN (Radio Access Network).

The Control Plane Function (CPF) node shown in FIG. 3 may perform all ora part of the MME (Mobility Management Entity) function of the fourthgeneration mobile communication, and all or a part of the control planefunction of the Serving Gateway (S-GW) and the PDN-gateway (P-GW) of thefourth generation mobile communication. The CPF node includes an Accessand Mobility Management Function (AMF) node and a Session ManagementFunction (SMF) node.

The user plane function (UPF) node shown in the figure is a type of agateway over which user data is transmitted and received. The UPF nodemay perform all or part of the user plane functions of the S-GW and theP-GW of the fourth generation mobile communication.

The PCF (Policy Control Function) node shown in FIG. 2 is configured tocontrol a policy of the service provider.

The illustrated Application Function (AF) node refers to a server forproviding various services to the UE.

The Unified Data Management (UDM) node as shown refers to a type of aserver that manages subscriber information, like an HSS (Home SubscriberServer) of 4th generation mobile communication. The UDM node stores andmanages the subscriber information in the Unified Data Repository (UDR).

The Authentication Server Function (AUSF) node as shown authenticatesand manages the UE.

The Network Slice Selection Function (NSSF) node as shown refers to anode for performing network slicing as described below.

FIG. 3a is an exemplary diagram illustrating an architecture forsupporting a multiple PDU session through two data networks. FIG. 3b isan exemplary diagram illustrating an architecture for supporting aconcurrent access through two data networks.

FIG. 3a illustrates an architecture that allows an UE to simultaneouslyaccess two data network using a multiple PDU session. Two SMFs may beselected for two different PDU sessions.

FIG. 3b illustrates an architecture that allows the UE to simultaneouslyaccess two data networks using one PDU session.

<Network Slice>

The following describes the slicing of the network to be introduced inthe next generation mobile communication.

Next-generation mobile communication introduces the concept of networkslicing in order to provide various services through a single network.In this connection, slicing a network refers to a combination of networknodes with the functions needed to provide a specific service. Thenetwork node that constitutes the slice instance may be a hardwareindependent node, or it may be a logically independent node.

Each slice instance may consist of a combination of all the nodes neededto construct the entire network. In this case, one slice instance alonemay provide service to the UE.

Alternatively, the slice instance may consist of a combination of someof the nodes that make up the network. In this case, the slice instancemay provide service to the UE in association with other existing networknodes without the slice instance alone providing the service to the UE.In addition, a plurality of slice instances may cooperate with eachother to provide the service to the UE.

The slice instance may differ from a dedicated core network in that allnetwork nodes, including the core network (CN) node and the RAN may beseparated from each other. Further, the slice instance differs from thededicated core network in that the network nodes may be logicallyseparated.

<Roaming in Next Generation Mobile Communication Network>

Meanwhile, there are two schemes for handling a signaling request fromthe UE in a situation where the UE roams in a visited network, forexample, Visited Public Land Mobile Network (VPLMN). A local break out(LBO) being a first scheme handles a signaling request from the UE by avisited network. According to a Home Routing (HR) being a second scheme,the visited network transfers a signaling request from the UE to a homenetwork of the UE.

FIG. 4a is an exemplary diagram illustrating an architecture to whichthe LBO scheme is applied during roaming. FIG. 4b is an exemplarydiagram illustrating an architecture to which the HR scheme is appliedduring roaming.

As shown in FIG. 4a , in an architecture to which the LBO scheme isapplied, user data are transferred to a data network in a VPLMN. To thisend, a PCF in the VPLMN performs interaction with an AF in order togenerate a PCC rule for a service in the VPLMN. A PCF node in the VPLMNcreates a PCC rule based on a policy set insided according to a roamingconvention with a Home Public Land Mobile Network (HPLMN) businessman.

As shown in FIG. 4b , in the architecture to which the HR scheme isapplied, data of the UE is transferred to a data network in the HPLMN.

<Data Bypass to Non-3GPP Network>

In the next generation mobile communication, the data of the UE maybypass to a non-3GPP network, for example, a Wireless Local Area Network(WLAN) or Wi-Fi.

FIG. 5a to FIG. 5f illustrate architectures for bypassing data to thenon-3GPP net work.

The Wireless Local Area Network (WLAN) or Wi-Fi is regarded as theuntrusted non-3GPP network. In order to access the non-3GPP network to acore network, a Non-3GPP InterWorking Function (N3IWF) may be added.

<Interworking with Existing 4 Generation (G) Mobile CommunicationSystem>

Although the UE escapes from coverage of a next generation Radio AccessNetwork (RAN), the UE may receive a service through a 4 G mobilecommunication system. The above refers to interworking. Hereinafter, theinterworking will be described in detail.

FIG. 6a illustrates an architecture for interworking when the UE doesnot roam, and FIG. 6b illustrates an architecture for interworking whenthe UE roams.

Referring to FIG. 6a , when the UE does not roam, an E-UTRAN and an EPCfor existing 4G LTE and a 5G mobile communication network may interworkwith each other. In FIG. 6a , a Packet data network Gateway (PGW) for anexisting EPC is divided into a PGW-U being responsible for only a userplane and a PGW-C being a control plane. Further, the PGW-U merges withan UPF of a 5G core network. The PGW-C merges with an SMF of the 5G corenetwork. In addition, a Policy and Charging Rules Function (PCRF) for anexisting EPC may merge with a PCF of the 5G core network. An HSS for theexisting EPC may merge with an UDM of the 5G core network. Although theUE may access a core network through the E-UTRAN, the UE may access acore network through a radio access network (RAN) and an AMF.

Referring to FIG. 6a and FIG. 6b to compare with each other, when the UEroams a Visited Public Land Mobile Network (VPLMN), the data of the UEare transferred through a Home PLMN (HPLMN).

Meanwhile, an N26 interface shown in FIG. 6a and FIG. 6b is an interfaceconnected between an MME and an AMF for easy interworking between an EPCand an NG. The N26 interface may be selectively supported according to abusinessman. That is, for interworking with an EPC, a networkbusinessman may provide an N26 interface or may not provide the N26interface.

During a roaming situation, the UE transmits a PDU session establishmentrequest message to the network. If the UE receives a response thereto,the UE may know that the PDU session is established. However, the UEcannot know whether the PDU session is established in a Local Breakout(LBO) scheme or a Home Routed (HR) scheme. Accordingly, the handover maynot be performed. However, since the UE cannot know whether or not areal handover can succeed. In this case, unnecessary signaling occurs.

SUMMARY OF THE INVENTION

The prevent invention has been made in an effort to solve theabove-described problems.

To achieve the foregoing purposes, the disclosure of the presentspecification proposes a method for handling a packet data unit (PDU)session establishment procedure. The method may be performed by anaccess and mobility management function (AMF) node and comprise:determining whether to reject a PDU session establishment request. Thedetermination may be performed if the PDU session establishment requestincludes an existing PDU session identifier. Based on the existing PDUsession identifier, an identifier of a session management function (SMF)node may be acquired. The PDU session establishment request may beaccepted, if it is determined based the identifier of the SMF node thatthe SMF node and the AMF node belong to a same PLMN. The PDU sessionestablishment request may be further accepted, if it is determined basedthe identifier of the SMF node that the SMF node belongs to a HPLMN. ThePDU session establishment request may be rejected, if it is determinedbased the identifier of the SMF node that the SMF node and the AMF nodedo not belong to the same PLMN or the SMF node does not belong to theHPLMN.

The PDU session establishment request message may further comprise arequest type. The request type may indicate an “initial request” toconfigure a new PDU session, or the request type may indicate an“existing PDU session” where there is the existing PDU session.

When the request type indicates the “existing PDU session”, movement ofa PDU session may be requested between a 3rd Generation PartnershipProject (3GPP) based access network and a non-3GPP based access network.

The AMF node may store an identifier of a PDU session and the identifierof the SMF node in connection with each other.

The identifier of the SMF node may comprise an identifier of a PLMN.

The method may further comprise: transmitting a message including arejection cause when the PDU session establishment request is rejected.

To achieve the foregoing purposes, the disclosure of the presentspecification proposes an access and mobility management function (AMF)node for handling a packet data unit (PDU) session establishmentprocedure. The AMF node may comprise: a transceiver; and a processor tocontrol the transceiver, and to determine whether to reject a PDUsession establishment request. The determination may be performed if thePDU session establishment request includes an existing PDU sessionidentifier. Based on the existing PDU session identifier, an identifierof a session management function (SMF) node may be acquired. The PDUsession establishment request may be accepted, if it is determined basedthe identifier of the SMF node that the SMF node and the AMF node belongto a same PLMN. The PDU session establishment request may be furtheraccepted, if it is determined based the identifier of the SMF node thatthe SMF node belongs to a HPLMN. The PDU session establishment requestmay be rejected, if it is determined based the identifier of the SMFnode that the SMF node and the AMF node do not belong to the same PLMNor the SMF node does not belong to the HPLMN.

According to the disclosure of the present invention, the problem of theconventional technology described above may be solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of an evolved mobile communicationnetwork.

FIG. 2 is an exemplary diagram illustrating a predicted structure of anext generation mobile communication in terms of a node.

FIG. 3a is an exemplary diagram illustrating an architecture forsupporting a multiple PDU session through two data networks, and FIG. 3bis an exemplary diagram illustrating an architecture for supporting aconcurrent access through two data networks.

FIG. 4a is an exemplary diagram illustrating an architecture to whichthe LBO scheme is applied during roaming, and FIG. 4b is an exemplarydiagram illustrating an architecture to which the HR scheme is appliedduring roaming.

FIG. 5a to FIG. 5f illustrate architectures for bypassing data to thenon-3GPP network.

FIG. 6a illustrates an architecture for interworking when the UE doesnot roam, and FIG. 6b illustrates an architecture for interworking whenthe UE roams.

FIG. 7 is a flowchart illustrating an exemplary registration procedure.

FIG. 8 is a flowchart illustrating an exemplary PDU sessionestablishment procedure.

FIG. 9 is a flowchart illustrating a registration procedure through auntrusted non-3GPP access.

FIG. 10 is a flowchart illustrating a PDU session procedure of UEthrough a untrusted non-3GPP access.

FIG. 11a illustrates a PDU session handover procedure to a 3GPP accessfrom a untrusted non-3GPP access.

FIG. 11b illustrates a PDU session handover procedure to a untrustednon-3GPP access from a 3GPP access.

FIG. 12 is a flowchart illustrating a method of indicating whether a PDUsession is established in a LBO scheme or an HR scheme according to afirst disclosure of the present specification.

FIG. 13 is a flowchart illustrating a method of indicating whetherhandover to the UE is possible during a registration procedure accordingto a second disclosure of the present specification.

FIG. 14 is a flowchart illustrating a method of controlling an operationof the UE by transmitting a message including a rejection cause valuewith respect to a PDU session establishment request for handoveraccording to a third disclosure of the present specification.

FIG. 15 is a flowchart illustrating a method of indicating whether acorresponding PDU session can perform HO during a PDU sessionestablishment procedure.

FIG. 16 is a block diagram illustrating a configuration of UE and anetwork according to an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention is described in light of UMTS (Universal MobileTelecommunication System) and EPC (Evolved Packet Core), but not limitedto such communication systems, and may be rather applicable to allcommunication systems and methods to which the technical spirit of thepresent invention may apply. The technical terms used herein are used tomerely describe specific embodiments and should not be construed aslimiting the present invention. Further, the technical terms used hereinshould be, unless defined otherwise, interpreted as having meaningsgenerally understood by those skilled in the art but not too broadly ortoo narrowly. Further, the technical terms used herein, which aredetermined not to exactly represent the spirit of the invention, shouldbe replaced by or understood by such technical terms as being able to beexactly understood by those skilled in the art. Further, the generalterms used herein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the specification includes themeaning of the plural number unless the meaning of the singular numberis definitely different from that of the plural number in the context.In the following description, the term ‘include’ or ‘have’ may representthe existence of a feature, a number, a step, an operation, a component,a part or the combination thereof described in the specification, andmay not exclude the existence or addition of another feature, anothernumber, another step, another operation, another component, another partor the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

In the drawings, user equipments (UEs) are shown for example. The UE mayalso be denoted a terminal or mobile equipment (ME). The UE may be alaptop computer, a mobile phone, a PDA, a smartphone, a multimediadevice, or other portable device, or may be a stationary device such asa PC or a car mounted device.

<Session and Service Continuity (SSC)>

A next generation mobile communication network provides various modes inorder to support the SSC.

1) SSC Mode 1

An UPF functioning as a PDU session anchor during the PDU sessionestablishment procedure is maintained regardless of an access technology(that is, access type and cell). In a case of an IP type PDU session, IPcontinuity is supported regardless of movement of the UE. The SSC mode 1is applicable to a certain PDU session type and a certain access type.

2) SSC Mode 2

When the PDU session includes one PDU session anchor, the networktriggers release of the PDU session, and may instruct the UE toestablish the same PDU session. During an establishment procedure of thenew PDU session, an UPF functioning as a PDU session anchor may be newlyselected. The SSC mode 2 is applicable to a certain PDU session type anda certain access type.

3) SSC Mode 3

With respect to a PDU session regarding the SSC mode 3, the network mayallow connection establishment of UE using a new PDU session withrespect to the same data network before releasing connectivity betweenthe UE and a previous PDU session anchor. When a trigger condition isapplied, the network may determine whether to select a PDU sessionanchor, that is, UPF suitable for a new condition of the UE. The SSCmode 3 is applicable to a certain PDU session type and a certain accesstype.

4) Selection of SSC Mode

In order to determine a type of an SSC mode associated with anapplication or an application group of the UE, an SSC mode selectionpolicy may be used.

The businessman may provide the SSC mode selection policy to the UE. TheSSC mode selection policy may include at least one SSC mode selectionpolicy rule.

<Registration Procedure>

The UE needs to obtain authorize to allow mobility tracking and datareception and to receive a service. To this end, the UE should registerin the network. A registration procedure is performed when the UE needsto perform an initial registration with respect to a 5G system. Further,when the UE needs to perform a periodic registration update, to move anew tracking area (TA) in an idle mode, and to perform a periodicregistration update, the registration procedure is performed.

During an initial registration procedure, an ID of the UE may beacquired from the UE. The AMF may transfer a PEI (IMEISV) to a UDM, anSMF, and a PCF.

FIG. 7 is a flowchart illustrating an exemplary registration procedure.

1) The UE may transmit an AN message to an RAN. The AN message mayinclude AN parameters and a registration request message. Theregistration request message may include information such as aregistration type, a subscriber permanent ID or a temporary user ID, asecurity parameter, an NSSAI, 5G ability of UE, PDU, and a PDU sessionstate.

In a case of the 5G RAN, the AN parameter may include a SUPI or atemporary user ID, a selected network and an NSSAI.

The registration type may indicate whether UE is “initial registration”(that is, UE is in a non-registration state), “mobility registrationupdate” (that is, UE is in a registered state to start the registrationprocedure due to mobility) or “regular registration update” (that is, UEis in a registered state to start the registration procedure due toperiodic update timer expiration). When the temporary user ID isincluded, the temporary user ID indicates a final serving AMF. When theUE is previously registered through a non-3GPP access in a PLMNdifferent from a PLMN of a 3GPP access, the UE may not provide an UEtemporary ID assigned by an AMF during a registration procedure througha non-3GPP access.

The security parameter may be used for authentication and integrityprotection.

The PDU session state represents a PDU session available (preset) in theUE.

2) When an SUPI is included or the temporary user ID does not representa valid AMF, the RAN may select the AMF based on the (R)AT and theNSSAI.

When the (R)AN cannot select a suitable AMF, the UE selects a temporaryAMF according to a local policy, and transfers a registration request tothe selected AMF. When the selected AMF cannot serve the UE, theselected AMF selects another suitable AMF for UE.

3) The RAN transmits an N2 message to a new AMF. The N2 message includesan N2 parameter and a registration request. The registration request mayinclude a registration type, a subscriber permanent identifier or atemporary use ID, a security parameter, an NSSAI, and an MICO mode basicsetting.

When the 5G-RAN is used, the N2 parameter includes location informationon a cell on which UE camps, cell identifier, and an RAT type.

If a registration type indicated by UE is periodic registration update,following procedures 4 to 17 may not be performed.

4) The newly selected AMF may transmit an information request message toa previous AMF.

When a temporary user ID of the UE is included in a registration requestmessage and a serving AMF is changed after a final registration, the newAMF may transmit an information request message including completeregistration request information to the previous AMF in order to requestthe SUPI and the MM context.

5) The previous AMF transmits an information response message to thenewly selected AMF. The information response message may include theSUPI and the MM context, and SMF information.

In detail, the previous AMF transmits an information response messageincluding the SUPI and MM context.

When the previous AM includes information on an active PDU session, theprevious AMF may add SMF information including an ID and a PDU sessionID of the SMF to the information response message.

6) When the SUPI is not provided by the UE or is not searched from theprevious AMF, the new AMF transmit an Identity Request message to theUE.

7) The UE transmits an Identity Response message including the IdentityResponse to the new AMF.

8) The AMF may determine to trigger an AUSF. In this case, the AMF mayselect an AUSF based on the SUPI.

9) The AUSF may start authentication of the UE and NAS securityfunction.

10) The new AMF may transmit an information response message to theprevious AMF.

If the AMF is changed, the new AMF may transmit the information responsemessage in order to confirm transfer of a UE MM context.

If authentication/security procedure fails, a registration is rejectedand the new AMF may transmit a rejection message to the previous AMF.

11) The new AMF may transmit an Identity Request message to the UE.

When a PEI is not provided by the UE or the PEI is not searched from theprevious AMF, the AMF may transmit an Identity Request message in orderto search the PEI.

12) The new AMF tests an ME identifier.

13) If a procedure 14 to be described later is performed, the new AMFselects a UDM based on the SUPI.

14) If an AMF is changed after final registration, a valid subscriptioncontext with respect to the UE is not included in the AMF, or the UEprovides the SUPI which does not refer to a valid context, the new AMFstarts an update location procedure. Alternatively, the UDM starts acancel location with respect to a previous AMF, the new AMF may start anupdate location procedure. The previous AMF removes the MM context tonotify to all possible SMF(s). The new AMF obtains AMF relationsubscription data from the UDM to generate an MM context with respect tothe UE.

When network slicing is used, the AMF acquires an NSSAI allowed based onthe requested NSSAI, UE subscription and local policy. If it is notsuitable to support an NSSAI in which the AMF is allowed, theregistration request is again routed.

15) The new AMF may select a PCF based on the SUPI.

16) The new AMF transmit a UE Context Establishment Request message tothe PCF. The AMF may request an operator policy with respect to the UEto the PCF.

17) The PCF transmits a UE Context Establishment Acknowledged message tothe new AMF.

18) The new AMF transmits an N11.

In detail, if the AMF is changed, the new AMF notifies a new AMF servingthe UE to each SMF. The AMF verifies a PDU session state from the UE asavailable SMF information. When the AMF is changed, available SMFinformation may be received from the previous AMF. The new AMF mayrequest to the SMF to release a network resource associated with a PDUsession which is not activated in the UE.

19) The new AMF transmits a N1 response message to the SMF.

20) The previous AMF transmits a UE Context Termination Request messageto the PCF.

When the previous AMF is previously requested so that a PDF PCFconfigures the UE context.

21) The PCF may transmit the UE Context Termination Request message tothe previous AMF.

22) The new AMF transmits a registration accept message to the UE. Theregistration accept message may include a temporary user ID, aregistration area, mobility limitation, a PDU session state, an NSSAI, aregular update timer and an allowed MICO mode.

When the AMF assigns a new temporary user ID, the temporary user ID maybe further included in the registration accept message. When themobility limitation is applied to the UE, information indicating themobility limitation may be further included in the registration acceptmessage. The AMF may add information indicating a PDU session state withrespect to the UE to the registration accept message. The UE may removea temporary internal resource associated with a PDU session which is notindicated as activation in the received PDU session state. If PDUsession state information is included in a Registration Request, the AMFmay add information indicating a PDU session state the UE to theregistration accept message.

23) The UE transmits a registration complete message to the new AMF.

<PDU Session Establishment Procedure>

The PDU session establishment procedure may include two types of PDUsession establishment procedures

-   -   PDU session establishment procedure starting by UE    -   PDU session establishment procedure starting by a network. To        this end, the network may transmit a device trigger message to        application(s) of the UE.

FIG. 8 is a flowchart illustrating an exemplary PDU sessionestablishment procedure.

It is assumed in a procedure shown in FIG. 8 that the UE is previouslyregistered on the AMF according to a registration procedure shown inFIG. 7. Accordingly, it is assumed that the AMF previously acquires usersubscription data from the UDM.

1) The UE transmits an NAS message to the AMF. The message may includean S-NSSAI, a DNN, a PDU session ID, a request type, and N1 SMinformation.

In order to establish the new PDU session, the UE may create a new PDUsession ID.

The UE may start a PDU session establishment procedure starting by theUE by transmitting an NAS message obtained by adding the PDU sessionestablishment request message to N1 SM information. The PDU sessionestablishment request message may include a request type, an SSC mode,and a protocol configuration option.

However, the PDU session establishment is to configure a new PDUsession, a request type represents “initial request”. However, whenthere is an existing PDU session between a 3GPP access and a non-3GPPaccess, the request type may represent “existing PDU session”.

The NAS message transmitted by the UE is encapsulated in the N2 messageby an AN. The N2 message is transmitted to the AMF, and may include userlocation information and access technology type information.

-   -   N1 SM information may include SM PDU DN request container        including information on PDU session authentication by external        DN.

2) The AMF may determine that a message corresponding to a request withrespect to a new PDU session when the request type indicates “initialrequest” and the PDU session ID is not sued for an existing PDU sessionof UE and the PDU session ID is not used for an existing PDU session ofthe UE.

If the NAS message does not include the S-NSSAI, the AMF may determine adefault S-NSSAI with respect to a requested PDU session according to UEsubscription. The AMF may store a PDU session ID and an ID of an SMF inconnection with each other.

3) The AMF transmits an SM request message to the SMF. The SM requestmessage may include a subscriber permanent ID, a DNN, an S-NSSAI, a PDUsession ID, an AMF ID, N1 SM information, user location information, andan access technology type. The N1 SM information may include a PDUsession ID and a PDU session establishment request message.

The AMF ID is used to identify an AMF serving the UE. The N1 SMinformation may include a PDU session establishment request messagereceived from the UE.

4a) The SMF transmits a subscriber data request message to the UDM. Thesubscriber data request message may include a subscriber permanent IDand a DNN.

During the procedure 3, when the request type indicates “existing PDUsession, the SMF determines that a corresponding request is causedbetween a 3GPP access and a non-3GPP access. The SMF may identify anexisting PDU session based on a PDU session ID.

When the SMF does not search SM relation subscription data with respectto the UE associated with the DNN yet, the SMF may request subscriptiondata.

4b) The UDM may transmit the subscription data response data to the SMF.

The subscription data may include information on an authenticatedrequest type, an authenticated SSC mode, and a basic QoS profile.

The SMF may configure whether a UE request complies with usersubscription and local policy. Alternatively, the SMF rejects a UErequest through NAS SM signaling (including related SM rejection cause),and reports that the PDU session ID is regarded to be released to theAMF.

5) The SMF transmits a message to a DN through a UPF.

In detail, when the SMF approves/authenticates a PDU sessionestablishment, the SMF selects a UPF to trigger a PDU.

When the PDU session establishment authentication/right grant fails, theSMF finishes the PDU session establishment procedure to report rejectionto the UE.

6a) if a dynamic PCC is distributed, the SMF selects the PCF.

6b) The SMF may start a PDU-CAN session establishment in a direction ofthe PCF in order to obtain a basic PCC rule with respect to a PDUsession. If the request type during the procedure 3 represents the“existing PDU session”, the PCF may start PDU-CAN session modification.

7) If the request type during the procedure 3 represents the “initialrequest”, the SMF selects an SSC mode with respect to the PDU session.If a procedure 5 is not performed, the SMF may also select the UPF. In acase of the request type IPv4 or IPv6, the SMF may assign IPaddress/prefix with respect to a PDU session.

8) When a dynamic PCC is disposed and a PDU-CAN session establishment isnot terminated yet, the SMF may starts a PDU-CAN session.

9) When the request type represents the “initial request” and theprocedure 5 is not performed, the SMF starts an N4 session establishprocedure using a selected UPF. Otherwise, the SMF may start an N4session modification procedure using a selected UPF.

9a) The SMF transmits an N4 session establishment/modification requestmessage to the UPF. Further, the SMF may provide packet detection,enforcement and report rule to be installed at the UPF with respect tothe PDU. When the CN tunnel information is assigned to the SMF, the CNtunnel information may be provided to the UPF.

9b) The UPF may respond by transmitting the N4 sessionestablishment/modification response message. When the CN tunnelinformation is assigned by the UPF, the CN tunnel information may beprovided to the SMF.

10) The SMF transmits the SM response message to the AMF. The SMresponse message may include a cause, N2 SM information, and N1 SMinformation. The N2 SM information may include a PDU session ID, a QoSprofile, and CN tunnel information. The N1 SM information may include aPDU session establishment accept message. The PDU session establishmentaccept message may include an allowed QoS rule, an SSC mode, an S-NSSAI,and an assigned IPv4 address.

The N2 SM information is information where the AMF should transfer tothe RAN, and may include the following information.

-   -   CN tunnel information: The CN tunnel information corresponds to        a core network address of a N3 tunnel corresponding to the PDU        session.    -   QoS profile: The QoS profile is used to provide mapping between        a QoS parameter and a QoS flow identifier to the RAN.    -   PDU session ID: The PDU session ID may be used to indicate a        relationship between AN resources with respect to the UE and the        PDU session by AN signaling with respect to the UE.

Meanwhile, the N1 SM information includes a PDU session accept messageto be provided to the UE from the AMF.

Multiple QoS rules may be included in N1 SM information and N2 SMinformation of the PDU session establishment accept message.

-   -   The SM response message include information to determine which        access is used so that a PDU session ID and the AMF are used for        a certain UE and the UE.

11) The AMF transmits an N2 PDU session request message to the RAN. TheN2 PDU session request message may include N2 SM information and an NASmessage. The NAS message may include a PDU session ID and a PDU sessionestablishment accept message.

The AMF may transmit a NAS message including a PDU session ID and a PDUsession establishment accept message. Further, the AMF adds the N2 SMinformation from the SMF to the N2 PDU session request message totransmit N2 PDU session request message the RAN.

12) The RAN may specific signal exchange with the UE associated withinformation received from the SMF.

Further, the RAN assigns RAN N3 tunnel information with respect the PDUsession.

The RAN transfers the NAS message provided during the procedure 10 tothe UE. The NAS message may include a PDU session ID and N1 SMinformation. The N1 SM information may include a PDU sessionestablishment accept message.

When a necessary RAN resource is configured and the RAN tunnelinformation is successfully assigned, the RAN transmits the NAS messageto the UE.

13) The RAN transmits the N2 PDU session response message to the AMF.The N2 PDU session response message may include a PDU session ID, acause, and N2 SM information. The N2 SM information may include a PDUsession ID, (AN) tunnel information, and an allowed/rejected QoS profilelist.

-   -   RAN tunnel information may correspond to an access network        address of a N3 tunnel corresponding to the PDU session.

14) The AMF may transmit an SM request message to the SMF. The SMrequest message may include N2 SM information. Here, the AMF maytransfer the N2 SM information received from the RAN to the SMF.

15a) When an N4 session with respect to the PDU session is not previousconfigured, the SMF may start the N4 session establishment proceduretogether with the UPF. Otherwise, the SMF may start an N4 sessionmodification procedure using the UPF. The SMF may provide AN tunnelinformation and CN tunnel information. The CN tunnel information may beprovided only when the SMF selects the CN tunnel information during aprocedure 8.

The UPF may transmit an N4 session establishment/modification responsemessage to the SMF.

16) The SMF may transmit an SM response message to the AMF. If the aboveprocedure is terminated, the AMF may transfer a related event to theSMF. When the RAN tunnel information is changed or upon handover inwhich the AMF is redisposed, the related event occurs.

17) The SMF transmits information to the UE through a UPF. In detail, ina case of the PDU Type IPv6, the SMF creates an IPv6 RouterAdvertisement to transmit the IPv6 Router Advertisement through the N4and the UPF.

18) When the PDU session establishment request is caused due to handoverbetween a 3GPP access and a non-3GPP access, that is, if the requesttype is set as a “existing PDU session”, the SMF release a user planethrough a source access (3GPP access or non-3GPP access).

19) When an ID of the SMF is not included during a procedure 4b by anUDM of a DNN subscription context, the SMF may include the SMF addressand the DNN to call a “UDM_Register UE serving NF service”. The UDM maystore an ID and an address of the SMF, and a related DNN.

If the PDU session establishment fails during a procedure, the SMFreports the above to the AMF.

<Registration Procedure Through Untrusted Non-3GPP Access>

The following is a description of a registration procedure to a 5GCnetwork through a untrusted non-3GPP access network by the UE.

FIG. 9 is a flowchart illustrating a registration procedure through auntrusted non-3GPP access.

1) The UE accesses a untrusted non-3GPP access network, and receivesassignment of an IP address. During the above procedure, a predeterminednon-3GPP authentication method may be used. If the UE is determined toattach to a 5GC network, the UE discovers an IP of an N3IWF from a 5GPLMN.

2) The UE starts an IKEv2 signaling procedure to configure an IPsec SAtogether with an N3IWF. After a 2a procedure, all subsequent IKEv2messages are encrypted and integrity thereof is ensured. An N3IWF isoperated as an EAP authenticator to search a network access identifier(NAI) of the UE. During the procedure 2d, the UE may transfer aregistration type, a permanent user ID, or a 3GPP-unique Vendor Id (VID)payload including a temporary user ID and a registration parameter suchas a network slice and an NSSAI. When the UE is previously registered ina PLMN through a 3GPP access and an N3IWF selected during a procedure 1is not located at the PLMN, the UE may not include a temporary IDthereof in a registration parameter.

3) The N3IWF may select the AMF based on a received registrationparameter and a local policy. Next, instead of the UE, the N3IWF maycreate a registration request message to transmit the registrationrequest message to the AMF through an N2 interface. The registrationrequest message may include a registration parameter andEAP-RES/Identity. The registration request message is encapsulated in anN2 message. The N2 message may include an access type indicating the“trusted non-3GPP access”. If a temporary user ID of the UE is includedin the registration parameter, the AMF may request an SUPI and MMContext of the UE from another AMF.

4) The AMF may request authentication of the UE to an AUSF by selectingthe AUSF to send an Auth_Req message to the AUSF. The Auth_Req messagemay include EAP-RES/Identity. The AUSF should be operated as an EAPserver, and should select an EAP method for authenticating the UE. TheEAP method is determined based on UE subscription information andinformation included in an NAI of the UE. The AUSF may acquire UEsubscription information from the UDM.

5) An EAP based mutual authentication procedure is performed between theUE and the AUSF. According to a selected EAP authentication method, aplurality of EAP request/response messages may be transmitted betweenthe UE and the AUSFs. An EAP message may be in encapsulated in an IKEv2between the UE and the N3IWF. The EAP message is encapsulated in an NASauthentication request/response message between the N3IWF and the AMF,which may be sequentially encapsulated in N2 NAS DL/UL transmissionmessages. The EAP message may be encapsulated in an Auth_Req/Res messagebetween the AMF and the AUSF.

6a) If the EAP based mutual authentication procedure is successfullycompleted, the AUSF transmits an Auth_Res message to the AMF. TheAuth_Res message may include EAP success, security key. The security keymay include an NAS security key and at least one master session key usedin an AMF in order to create a security key (N3IWF).

6b) The AMF transmits a DL NAS Transport message to the N3IWF. The DLNAS Transport message may include an EAP success message, a security keyof N3IWF and a NAS security mode command (SMC). After the aboveprocedure, the N3IWF may create a UE context storing UE specificinformation such as UE identity or related N2 connection.

6c-6d) The N3IWF may transmit an IKE_AUTH response message to the UE.Accordingly, configuration of an IPsec SA is completed between the UEand the N3IWF. The IPsec SA (refers to “signaling IPsec SA”) may be usedto stably transmit the NAS message between the UE and the N3IWF. The NASmessage is encapsulated in a GRE through an IPsec. After a procedure 6c,the IKEv2 message may be transmitted to complete configuration of asignaling IPsec SA.

7) The N3IWF may transmit an NAS SMC request received from the AMFduring a procedure 6b through the configured IPsec SA to the UE. The UEtransmits an NAS SMC complete message. The NAS SMC complete message maybe included in an N2 UL NAS transmission message to be transferred tothe AMF.

8. The AMF adds an NAS registration approval message in an N2 initialcontext configuration request message to transmit the N2 initial contextconfiguration request message to the N3IWF. The N2 initial contextconfiguration request may be transferred to the UE through the IPsec SA.Finally, the UE adds the NAS registration complete message forwarded tothe AMF by the N3IWF to an N2 initial context configuration responsemessage to transmit the N2 initial context configuration responsemessage.

<PDU Session Establishment Procedure of UE Through Trusted Non-3GPPAccess>

The following is a description of a procedure of establishing a PDUsession through a non-3GPP access network which is not trusted.

FIG. 10 is a flowchart illustrating a PDU session procedure of UEthrough a trusted non-3GPP access.

First, it is assumed that the UE performs a registration procedure in a5GC network through a non-3GPP access network which is not trusted.

1) The UE transmit a PDU session establishment request message to theAMF. As described above with reference to FIG. 8, the PDU sessionestablishment request message may include an ID of a PDU session, arequest type, an SSC mode, and a protocol configuration option. The PDUsession establishment request message may be transmitted to the N3IWFthrough an IPsec SA configured for the NAS signal. The N3IWF transfersthe PDU session establishment request message to an AMF of a 5GCnetwork.

2a) A PDU session establishment procedure is performed through a 3GPPaccess.

2b) The AMF transmits an N2 PDU session establishment request message inorder to configure an access resource with respect to a PDU session tothe N3IWF. As described above with reference to FIG. 8, the PDU sessionestablishment request message may include an ID of the PDU, a requesttype, an SSC mode, and a protocol configuration option. Moreover, thePDU session establishment request message may include a QoS profile of apreviously allowed QoS rule of a requested PDU. In a case of a Q-typeQoS rule, a N2 PDU session request message includes a QoS parameter withrespect to the QoS profile. In addition, the N2 PDU session requestmessage includes a PDU session accept activation message to be forwardedto the UE.

3) Based on the QoS profile received at a previous step and a policy anda configuration, the N3IWF determines the number of IPsec child SAs tobe established and a QoS profile associated with an IPsec child SA. Forexample, the N3IWF configures the IPsec child SA to associated all QoSprofiles with the IPsec child SA. In this case, all QoS flows of the PDUsession may be transmitted through one IPsec child SA.

4a) The N3IWF transmits an IKE CREATE_CHILD_SA request message to the UEin order to establish a first IPsec child SA. The IKE CREATE_CHILD_SArequest message may include a 3GPP-unique VID payload. The VID payloadmay include a QoS profile associated with a child SA, an ID of a PDUsession associated with the child SA, and a DSCP value associated with achild SA. An IKE Create_Child_SA request message may include informationsuch as Traffic Selector (TS) for an SA payload N3IWF and the UE.

4b) If the UE accepts a new IPsec child SA, the UE transmit an IKECreate_Child_SA response message. While establishing the IPsec child SA,an IP address may not assigned to the UE yet.

4c-4d) During a procedure 3, when the N3IWF determines to establish aplurality of IPsec child SAs with respect to the PDU session. Theadditional IPsec child SAs may be connected with at least one QoSprofile.

5) If all IPsec child SAs are established, a PDU session establishmentaccept message received by step 2 b to the UE through an IPsec SA forsignaling NAS.

6) The N3IWF transmits an N2 PDU session request acknowledge (Ack) tothe AMF.

7) A PDU session establishment procedure is performed through a 3GPPaccess.

8) In a user plane,

When the UE transmits a UL PDU, the UE determines a QoS profilerassociated with the UL PDU (using a QoS rule of a session in a PDU).Furthermore, the UE may encapsulate the UL PDU in a GRE packet totransmit the GRE packet to the N3IWF through the IPsec child SAassociated with the QoS profile. A header of the GRE packet istransmitted to a QoS profile associated with the UL PDU.

-   -   If the N3IWF receives a DL PDU through an N3, the N3IWF uses QoS        marking and an identifier of the PDU session in order to        determine the IPSec child SA. The N3IWK encapsulates the DL PDU        in the GRE packet to copy the QoS marking to a header of the GRE        packet. Accordingly, the N3IWF may add a Reflective QoS        Indicator (RIFT) to be used by the UE to the GRE header.

<PDU Session Handover Procedure Between 3GPP Access and Trusted Non-3GPPAccess>

FIG. 11a illustrates a PDU session handover procedure to a 3GPP accessfrom a trusted non-3GPP access.

Referring to FIG. 11a , when the UE is not registered in a 3GPP access,the UE performs a registration procedure.

Further, the UE performs a PDU session establishment procedure.

FIG. 11b illustrates a PDU session handover procedure to a trustednon-3GPP access from a 3GPP access.

Referring to FIG. 11b , when the UE is not registered in a trustednon-3GPP access, the UE performs a registration procedure.

In addition, the UE perform a PDU session establishment procedure.

<Discloses of the Present Specification>

In a roaming situation, if the UE transmits a PDU session establishmentrequest message to a network to receive a response thereto, it may beknown that a PDU session is established. However, the UE cannot knowwhether a PDU session is established in a Local Breakout (LBO) scheme ora Home Routed (HR) scheme. In order to perform handover between 3GPP andnon-3GPP, the same SMF is basically selected in UEs so that the sameUPF/IP address may be assigned. After the UE establishes the PDU sessionin an LBO scheme through a 3GPP access in a roaming situation, the UEshould create a PDU session in an LBO scheme at a non-3GPP access tohandover to the non-3GPP. However, when the handover is not consideredand the PDU session is created, a problem may occur. For example, anN3IWF for a non-3GPP access is selected, the UE may select an N3IWF inan HPLMN instead of an N3IWF in a VPLMN providing a service to the UE.In this case, a PDU session is created in a LBO scheme in the 3GPPaccess and the PDU session is created in a non-roaming scheme in anon-3GPP access so that handover may not be performed. However, sincethe UE cannot know whether or not real handover is successfullyperformed so that the handover may be attempted. In this case,unnecessary signaling occurs.

Accordingly, the disclosure of the present specification providesmethods for solving the above problems.

I. First disclosure: method of reporting whether a corresponding PDUsession is established in an LBO scheme or an HR scheme whileestablishing the PDU session

Now, the UE cannot know whether a corresponding PDU session is createdin an LBO scheme or an HR scheme when creating the PDU session. Thefirst disclosure suggests that a network node (e.g., SMF) includeinformation indicating which scheme a PDU session is created in a PDUSession Establishment Accept message. When the UE performs registrationthrough 3GPP access/non-3GPP access, the UE knows in which PLMN the UEis registered, if the UE knows PLMN information and a scheme (that is,LBO scheme or HR scheme) used to establish the PDU session, the UE maydetermine whether handover (HO) is possible.

a) First, when the UE is registered through a 3GPP access,

-   -   The UE performs N3IWF selection before registering in a non-3GPP        access. If it is determined that an N3IWF selected by the        selection procedure is located at the same PLMN as that of the        3GPP access, and the registration is successfully completed, the        UE may determine that the PDU session can handover regardless of        whether a scheme used to establish the PDU session is an LBO        scheme or an HO scheme.    -   However, if it is determined that the N3IWF selected by the        selection procedure is located at a PLMN different from a 3GPP        and the registration is successfully completed, only when a PDU        session of the 3GPP access is established in an HR scheme, the        UE may determine that the PDU session can handover.

b) When the UE is firstly registered through an non-3GPP access,

-   -   when the UE knows during registering in a 3GPP access that the        UE is successfully registered in the same PLMN as a PLMN in        which the N3IWF for non-3GPP access is located, the UE may        determine that the PDU session can handover regardless of        whether a scheme used to establish the PDU session is an LBO        scheme or an HO scheme.    -   When the UE knows during registering in a 3GPP access that the        UE is successfully registered in a PLMN different from a PLMN in        which the N3IWF for non-3GPP access is located, only when a PDU        session through an non-3GPP access is established in an HR        scheme, the UE may determine that the PDU session can handover.

Meanwhile, an SMF may transmit information or indicator (e.g., HOindication) indicating which handover is possible instead of directlyreporting whether the scheme is an HO scheme or a LBO scheme. Forexample, the SMF may transmit HO indication indicating that handover ispossible with respect to PDU sessions created through handover.

If the UE receives indication indicating that the handover is possible,the UE may perform handover whether a PDU session through a 3GPP sessionand a PDU session through a non-3GPP access are established in the samePLMN or in different PLMNs. If the information (or indicator) is notreceived, only when the PDU session through a 3GPP session and the PDUsession through a non-3GPP access are established in the same PLMN, theUE may perform the handover.

FIG. 12 is a flowchart illustrating a method of indicating whether a PDUsession is established in a LBO scheme or an HR scheme according to afirst disclosure of the present specification.

Referring to FIG. 12, the UE transmits a PDU session establishmentrequest message to the AMF. Referring to FIG. 8 and FIG. 10, the PDUsession establishment request message may include an ID of the PDU, arequest type, an SSC mode, and a protocol configuration option.

During a procedure 10, the SMF may include and transmit information oran indication indicating whether the PDU session is established in an HRscheme or an LBO scheme while transmitting a PDU session accept message.Further, the SMF may include and transmit an indication (e.g., HOIndication) indicating whether handover is possible. Although an exampleof FIG. 12 illustrates a procedure in 3GPP access, the above issimilarly applicable to the non-3GPP access.

II. Second disclosure: method of reporting whether to handover the PDUsession to the UE

According to the first disclosure described as above, the network shouldreport whether the PDU session is established in a LBO scheme or an HRscheme to the UE. However, since the first disclosure provides topologyinformation of a network, the first disclosure may be a scheme to whichbusinessmen do not prefer. The second disclosure suggests to report onlyinformation on which handover is possible to the UE instead of notproviding the same information of the first disclosure to the UE.

To this end, the UE may transfer an indication indicating thatregistration is performed for handover between a 3GPP access and anon-3GPP access when performing registration in another access forhandover. Further, the UE may transfer the indication together with anID of a PDU session to handover. The UE may report which PDU sessionhandovers by transferring an ID of the PDU session.

Accordingly, when the UE performs a registration procedure between a3GPP access and a non-3GPP access, the AMF acquires PDU sessioninformation from the UDM based on a PDU session ID received from the UE.Further, the AMF knows a PDU session ID to handover based on PDU sessioninformation acquired from the UDM. When PDU session information mappedto the PDU session ID is discovered, the AMF determines whether tohandover the PDU session based on context information. To this end, whenthe PDU session is created, the SMF may store information on whether acorresponding PDU session is established in an HR scheme or an LBOscheme in the UDM. That is, when SMF information and PDU information arestored during a procedure 19 of FIG. 12, the SMF may store informationon whether a corresponding PDU session is established in the HR schemeor the LBO scheme.

Meanwhile, as described above, the AMF may store an ID of the PDU and anID of the SMF in connection with each other. Accordingly, when the ID ofthe PDU session received from the UE indicates a previous PDU session,the AMF may discover an ID of the SMF stored in connection with the IDof the PDU session. Here, the ID of the SMF includes a PLMN ID.Accordingly, the AMF may know the AMF and the SMF are included in thesame PLMN or different PLMNs based on a PLMN ID extracted from the ID ofthe SMF. If the AMF and the SMF are located at the same PLMN in a statethat a roaming UE in 3GPP access handover-requests the 3GPP access PDUsession to a non-3GPP while being connected with the HPLMN at thenon-3GPP access, the UE may determine that a corresponding PDU sessionis established in the HR scheme. In this case, the AMF may determinethat handover is possible. Furthermore, if the AMF and the SMF arelocated at the HPLMN, the UE may determine that a corresponding PDUsession is established in the HR scheme. On the other hand, when it isdetermined that the AMF and the SMF are located at different PLMNs, theUE may determine that a corresponding PDU session is established in theLBO scheme. In this case, the UE may determine that the handover isimpossible.

Meanwhile, when the AMF knows that there is a PDU session mapped to aPDU session ID received from the UE, the AMF may select the SMF beingresponsible for a corresponding PDU session. When the AMF can transferSM signaling to the SMF, the AMF may determine that a corresponding PDUsession may handover. If there is a context with respect to the PDUsession, since the AMF cannot transfer SM signaling to the SMF when theSMF is located at a different PLMN, the AMF may determine that it isimpossible to handover a corresponding PDU session.

As shown in FIG. 5e , if both of the 3GPP access and the non-3GPP accessare connected with a PLMN different from the HPLMN, it may not determinewhether the a corresponding PDU session is established in the HR schemeor the LBO scheme based on only PLMN information. In this case, theabove determination may be performed based on PDU session informationstored in a UDM. When the AMF knows an HPLMN of the UE and an ID of theSMF includes a PLMN ID, the AMF may compare an HPLMN ID of the UE withPLMN ID extracted from an ID of the SMF to determine whether or not aPDU session is established in the HR scheme.

Although the UE does not report registration for handover, when the UEperforms initial registration or mobility registration, the AMF mayreport whether handover is possible by DNNs and/or S-NSSAIs whiletransferring a registration accept message to the UE.

That is, the AMF may report that the handover is possible between the3GPP access and a non-3GPP access while transmitting the registrationaccept message. The UE may be operated as follows based on whether thehandover is possible.

-   -   When the handover is possible, the UE performs the handover        procedure.    -   When the handover is impossible, the UE may determine whether to        perform an additional operation based on an SSC mode of the PDU        session.

For example, when a PDU session to be moved corresponds to a SSC mode 2based PDU session, the UE stops an existing PDU session to create a newPDU session through a newly accessed access network.

If a PDU session to be moved corresponds to a SSC mode 3 based PDUsession, the UE may request a new PDU session while maintaining anexisting PDU session through a newly accessed access network. Anapplication layer of the UE may move traffic to a newly created PDUsession by maintaining two sessions for a while. If a predetermined timeelapses or all traffics are moved to a new PDU session, the UE stops anexisting PDU session.

If a PDU session to be moved corresponds to a SSC mode 1 based PDUsession, the UE may perform an operation such as an SSC mode 3 or stopthe handover.

The AMF may not allow the registration and may transmit a registrationrejection message. In this case, a cause field of the registrationrejection message may include a cause value indicating that a HO isimpossible to be rejected.

FIG. 13 is a flowchart illustrating a method of indicating whetherhandover to the UE is possible during a registration procedure accordingto a second disclosure of the present specification.

As shown in FIG. 1 in a procedure 1 of FIG. 13, when the UE performs aregistration procedure in a new access for handover, the UE addsinformation of a handover indication and a PDU session to handover(e.g., PDU session ID) to a registration request message to send theregistration request message. Accordingly, as illustrated in a procedure22, the AMF transmits a registration accept message includinginformation indicating whether the handover is possible using the abovescheme. Although the above example indicates a procedure of 3GPP access,the above content is equally applicable to a non-3GPP.

III. Third disclosure: A method of controlling an operation of UE bytransmitting a rejection message including a rejection cause value withrespect to a PDU session establishment request of UE for handover.

According to the second disclosure, if the network reports informationon whether handover is possible, the UE directly determines based on theinformation to perform an operation of newly creating a PDU session.However, in this case, the network cannot control the UE in a desireddirection. Accordingly, a third disclosure of the present specificationis suggested as described below. In detail, if the UE transmit a PDUsession establishment request message for handover after performing aregistration procedure, the third disclosure determines whether the AMFcan perform handover. If it is determined that the handover isimpossible, the UE transmits a rejection message including a rejectioncause value. A method of determining whether the handover is possible isthe same as that described in the second disclosure. If a rejectioncause value is re-establish required, the UE may recognize that thehandover fails to request establishment of a new PDU session through anew approaching access network. If the rejection cause value indicatesthat the handover is impossible such as “handover not supported”, the UEstops the handover. The rejection cause value is determined based apolicy or a DNN configured by a businessman. For example, when an IMSDNN is used, the rejection cause value is re-establish required so thatthe UE may continuously receive the service. However, when an IoT DNN isused, the rejection cause value indicates ‘handover not supported’ sothat the UE may not perform the handover.

FIG. 14 is a flowchart illustrating a method of controlling an operationof the UE by transmitting a message including a rejection cause valuewith respect to a PDU session establishment request for handoveraccording to a third disclosure of the present specification.

Referring to FIG. 14, the UE transmits a PDU session establishmentrequest message to the AMF. As described above with reference to FIG. 8,FIG. 10, and FIG. 12, the PDU session establishment message may includean ID of a PDU, a request type, an SSC mode, and a protocolconfiguration option.

If the UE transmits a PDU session establishment request message, the AMFdetermines whether the handover is possible. In detail, as describedabove in the second disclosure, the AMF indicates that the request typein the received PDU session establishment request message is an“existing PDU session”. When a PDU session ID in the received PDUsession establishment request message indicates an ID of an existing PDUsession, the UE may determine whether the handover is possible.

In detail, as described above, the AMF may store the PDU session ID andthe ID of the SMF in connection with each other. Accordingly, when a PDUsession ID in the PDU session establishment request message receivedfrom the UE, the AMF may discover an ID of the SMF stored associatedwith the PDU session ID. Here, the ID of the SMF includes a PLMN ID.Accordingly, the AMF may know whether the AMF and the SMF are located atthe same PLMN or different PLMNs based on a PLMN ID extracted from theID of the SMF. If the AMF and the SMF are located at the same PLMN, theAMF may determine that a corresponding PDU session is established in theHR scheme. In this case, the AMF may determine that the handover ispossible. Further, if both of the AMF and the SMF are located at theHPLMN, the AMF may determine that a corresponding PDU session isestablished in the HR scheme. Conversely, when the AMF and the SMF arelocated at different HPLMNs, the AMF may determine that a correspondingPDU session is established in the LBO scheme.

Meanwhile, when a PDU session ID in the PDU session establishmentrequest message received from the UE indicates an existing PDU session,the AMF may select an SMF being responsible for a corresponding PDUsession. When SM signaling may be transferred to the SMF, the AMF maydetermine to handover a corresponding PDU session. If there is a contextwith respect to the PDU session, since the AMF cannot transfer the SMsignaling to the SMF when the SMF is located at a different PLMN, theAMF may determine that handover of the corresponding PDU session isimpossible.

Meanwhile, when the AMF does not know an existing PDU session indicatedby a PDU session ID in the PDU session establishment request messagereceived from the UE, the AMF may acquire information on the PDU sessionfrom the UDM. Moreover, the AMF may determine whether to handover thePDU session based on PDU session information acquired from the UDM.

When it is determined that the handover is impossible, the AMF mayinclude a rejection cause value in an MM NAS message to transmit the MMNAS message. The UE may determine a subsequent operation according tothe rejection cause value.

In detail, the UE may perform a following operation according to arejection cause value sent from the AMF.

(a) When the rejection cause value indicates ‘handover not supported’,‘HO is not allowed’ or ‘payload was not forwarded’,

the UE does not request the handover with respect to a corresponding PDUsession longer. Moreover, the UE may perform a following operation(until the PDU session stops, a PDU session is registration-released ina created PLMN, or an N3IWK is changed to a node included in anotherPLMN).

If a PDU session is in a SSC mode 1 or a SSC mode 3, the UE additionallycreates a PDU session having the same DNN/N-SSAI/SSC mode/PDU type asthose of the PDU session to handover through another access. The UE maywait until an application layer of a next UE moves a traffic included ina PDU session to handover to another access to release a previous PDUsession while remaining a new PDU session.

If the PDU session is an SSC mode 2, the UE may firstly stop the PDUsession to handover and establish a new PDU session through anotheraccess to request the service.

The UE may send an indication to request that the PDU session isestablished while requesting a new PDU session regardless of anoperation according to an SSC mode. In this case, an LBO is allowed insubscriber information of the UE according to a polity or setting of thebusinessman, the AMF may select a V-SMF and an H-SMF to create the PDUsession in an HR scheme. In this case, while the AMF selectivelytransmits a PDU session establishment request message to V-SMF/H-SMF,the UE may include indication indicating that the HR scheme isrequested. When the H-SMF receives the indication, informationindicating that the PDU session is created in a HR scheme may beincluded in the PDU session establishment accept message. In a case of aPDU session created by the above method, although the UE receives amessage including a rejection cause value indicating ‘HO is not allowedindication’ with respect to a PDU session having the same DNN/S-NSSAIform the AMF, the UE may again request handover. However, when the UEagain receives a message including a rejection cause value indicating‘HO is not allowed indication’ with respect to a PDU session from theAMF even if the UE transmits an indication to request to establish thePDU session in an HR scheme, the UE should not again request handoverwith respect to a PDU session having a corresponding DNN/S-NSSAI.

(b) When a rejection cause value indicates congestion.

When a rejection cause value in a message transmitted from the AMFindicates congestion, the message may include a back-off time valuetogether. The UE drives a back-off timer based on the back-off timevalue of a rejection message received from the AMF. Since this case isrejected due to congestion, the UE may not again attempt a request untila back-off timer is expired. That is, until the back-off timer isexpired, the UE does not again request the handover. Alternatively, ifthe AMF indicates that the rejection cause value is congestion but theUE knows that HO is not allowed through another indication, the UE maynot again request handover even if the back-off timer is expired. A nextoperation may be the same as that when a rejection cause value indicatesthat ‘HO is not allowed indication’.

Alternatively, although the rejection cause value indicates congestion,similar to a case where the rejection cause value indicates ‘HO is notallowed’, the UE may be operated.

IV. Fourth Disclosure: Method of allowing handover only when the UEconnects with a network through the same PLMN

When the UE performs a registration procedure through another accessnetwork for handover, a fourth disclosure of the present specificationmay handover a PDU session of the UE only when a 3GPP access network anda non-3GPP access network are located at the same PLMN. The fourthdisclosure does not need additional indication and procedure as comparedwith other disclosures. However, according to the situation, the UE maynot handover even if the handover is possible.

V. Fifth disclosure: Method of reporting whether a corresponding PDUsession ca n handover during a procedure of establishing PDU session

According to the fifth disclosure, the network may transmit informationdirectly indicating whether handover is possible or impossible insteadof not reporting information on whether a PDU session is established inan HR scheme or an LBO scheme. In this case, the UE may determinewhether to perform handover based on information indicating whether thehandover is possible while the UE does not know whether the PDU sessionis established in the HR scheme or the LBO scheme. For example, thenetwork may establish a plurality of PDU sessions by the same DNN. Amongthem, an SSC mode 1 based PDU session may indicate that handover ispossible, and an SSC mode 2/3 based PDU session may indicate that thehandover is impossible. In this case, the UE may handover only the SSCmode 1 based PDU session. In a case of the SSC mode 2, according todefinition of the SSC mode, after an existing PDU session stops, a newPDU session may be established. In this case, the handover is notperformed, a PDU session may stop through an existing access and a newPDU session may be established through a new access. Since a pluralityof parallel PDU session may be established for a predetermined time in acase of the SSC mode 3, a second PDU session is established through anew access while maintaining the first PDU session through a previousaccess, after a traffic is moved through a newly created second PDUsession, a previous first PDU session stops.

Alternatively, a PDU session created from the network is connected witha specific slice and a corresponding slice may be used in only aspecific access, the network may report that the handover is impossibleto the UE.

When using the method, when the UE previously completes registrationthrough both accesses, the SMF may previously report whether thehandover is possible to the UE. For example, it is assumed that the UEis registered in both of the 3GPP access and the non-3GPP access. Inthis case, if a current UE is registered in both of the 3GPP access andthe non-3GPP access through the same AMF, the AMF may report that theall the UEs are registered through one AMF to the SMF. The SMF mayreport that the handover is possible in a PDU session establishmentaccept message by taking into consideration an SSC mode based oninformation from the AMF. If the UEs complete the registration throughdifferent AMFs, one AMF cannot know whether the UEs are registered intwo accesses. Accordingly, in this case, the AMF send no information tothe SMF. Since the SMF does not receive information indicating that theUE completes a registration through two accesses from the AMF, the SMFmay add information indicating that the handover is impossible to a PDUsession establishment accept message.

FIG. 15 is a flowchart illustrating a method of indicating whether acorresponding PDU session can perform HO during a PDU sessionestablishment procedure.

Referring to FIG. 15, when the UE transmits a PDU session establishmentrequest message for handover during a procedure 1, the UE includeshandover indication (e.g., HO indication) in order to report a messageto be sent for handover to the AMF.

When the received message includes the HO indication, the AMF adds anindication (e.g., Simultaneous access indication) indicating whether theUE is simultaneously registered in a 3GPP access and a non-3GPP accessthrough one AMF to a PDU session establishment request message of theprocedure 3 to transmit the PDU session establishment request messagethe SMF.

During a procedure 10, the SMF may determine whether handover ispossible based on the indication (e.g., Simultaneous access indication).Although there is no indication, the SMF may determine whether thehandover is possible based on subscription information, UE abilityinformation, and the like.

The above embodiment may be implemented by hardware. The above isdescribed with reference to the accompanying drawings.

FIG. 16 is a block diagram illustrating a configuration of UE and anetwork according to an embodiment of the present invention.

As shown in FIG. 16, the UE 100 includes a storage unit 101, acontroller 120, and a transceiver 103. Further, the network node mayinclude one of an AMF, an SMF, an NEF, and an AF. The network node mayinclude a storage unit 511, a controller 512, and a transceiver 513.

The storage units store the above method.

The controllers control the storage units and the transceivers,respectively. In detail, the controllers execute the above methodsstored in the storage units, respectively. Further, the controllerstransmit the above signals through the transceiver.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method of handling a packet data unit (PDU)session establishment procedure, the method performed by an access andmobility management function (AMF) node and comprising: receiving a PDUsession establishment request; based on the PDU session establishmentrequest including an identifier of an existing PDU session, determiningan identifier of a session management function (SMF) node; determiningwhether to reject the PDU session establishment request based on theidentifier of the SMF node; and transmitting a message comprising arejection cause, based on a determination to reject the PDU sessionestablishment request, wherein determining whether to reject the PDUsession establishment request based on the identifier of the SMF nodecomprises: determining not to reject the PDU session establishmentrequest based on a determination that (i) the identifier of the SMF nodeand the AMF node belong to a same Public Land Mobile Network (PLMN), or(ii) the identifier of the SMF node belongs to a Home Public Land MobileNetwork (HPLMN).
 2. The method of claim 1, wherein the PDU sessionestablishment request message further comprises a request type, andwherein the request type indicates (i) an “initial request” to configurea new PDU session, or (ii) an “existing PDU session”.
 3. The method ofclaim 2, further comprising: based on the request type indicating the“existing PDU session”, requesting a movement of the existing PDUsession between a 3rd Generation Partnership Project (3GPP) based accessnetwork and a non-3GPP based access network.
 4. The method of claim 1,further comprising: storing the identifier of the existing PDU sessionand the identifier of the SMF node in association with each other. 5.The method of claim 1, wherein the identifier of the SMF node comprisesan identifier of a PLMN.
 6. The method of claim 1, wherein determiningthe identifier of the SMF node comprises: determining the identifier ofthe SMF node based on the identifier of the existing PDU session that isincluded in the PDU session establishment request.
 7. The method ofclaim 1, further comprising: determining to reject the PDU sessionestablishment request based on a determination that (i) the identifierof the SMF node and the AMF node do not belong to the same PLMN, and(ii) the identifier of the SMF node does not belong to the HPLMN.
 8. Anaccess and mobility management function (AMF) node configured to handlea packet data unit (PDU) session establishment procedure, the AMF nodecomprising: a transceiver; at least one processor; and at least onecomputer memory operably connectable to the at least one processor andstoring instructions that, when executed, cause the at least oneprocessor to perform operations comprising: receiving a PDU sessionestablishment request; based on the PDU session establishment requestincluding an identifier of an existing PDU session, determining anidentifier of a session management function (SMF) node; determiningwhether to reject the PDU session establishment request based on theidentifier of the SMF node; and transmitting a message comprising arejection cause, based on a determination to reject the PDU sessionestablishment request, wherein determining whether to reject the PDUsession establishment request based on the identifier of the SMF modecomprises: determining not to reject the PDU session establishmentrequest based on a determination that (i) the identifier of the SMF nodeand the AMF node belong to a same Public Land Mobile Network (PLMN), or(ii) the identifier of the SMF node belongs to a Home Public Land MobileNetwork (HPLMN).
 9. The AMF node of claim 8, wherein the PDU sessionestablishment request message further comprises a request type, andwherein the request type indicates (i) an “initial request” to configurea new PDU session, or (ii) an “existing PDU session”.
 10. The AMF nodeof claim 9, wherein the operations further comprise: based on therequest type indicating the “existing PDU session”, requesting amovement of the existing PDU session between a 3rd GenerationPartnership Project (3GPP) based access network and a non-3GPP basedaccess network.
 11. The AMF node of claim 8, wherein the operationsfurther comprise: storing the identifier of the existing PDU session andthe identifier of the SMF node in association with each other.
 12. TheAMF node of claim 8, wherein the identifier of the SMF node comprises anidentifier of a PLMN.
 13. The AMF node of claim 8, wherein theoperations further comprise: determining to reject the PDU sessionestablishment request based on a determination that (i) the identifierof the SMF node and the AMF node do not belong to the same PLMN, and(ii) the identifier of the SMF node does not belong to the HPLMN. 14.The AMF node of claim 8, wherein determining the identifier of the SMFnode comprises: determining the identifier of the SMF node based on theidentifier of the existing PDU session that is included in the PDUsession establishment request.